1. Technical Field
The present invention relates to a pneumatic tire.
2. Related Art
A pneumatic tire includes a carcass ply embedded as a reinforcing material. The carcass ply is generally configured to be wound up from inside to outside in a widthwise direction of a tire (hereinafter, referred to simply as “widthwise direction”) so as to wrap around a bead core with an end portion thereof. In contrast, JP-A-2007-131173, WO98/52777, and JP-A-7-315013 propose a configuration in which a carcass ply is wound up from the outside to the inside in the widthwise direction. By winding up the carcass ply from the outside to the inside in the widthwise direction, a distribution of a tensile force applied to the carcass ply is changed so as to increase a tensile force at a position which easily contributes to tire rigidity, and a steering stability performance of a tire is improved.
Specifically, JP-A-2007-131173 discloses a configuration in which steeering stability of a tire is improved by winding around the bead core with a single layer carcass ply from the outside to the inside in the widthwise direction so as to arrange an end portion of the carcass ply on the inside of the bead core in the radial direction of the tire (hereinafter, referred to simply as “radial direction”).
WO98/52777 discloses a tire intended to substantially reduce the frequency of occurrence of tire breakage in an early stage with a carcass ply wound up around bead cores from the outside to inside in the widthwise direction.
JP-A-07-315013 discloses an pneumatic radial tire capable of contributing to the weight reduction of the tire and maintenance of tire rigidity without lowering performances such as a steering stability by having a configuration that a carcass ply passes through outer surface sides of the tire with respect to bead fillers, and both end portions of the carcass ply are wound up around the bead cores on both sides from the outside toward the inside so as to be supported thereby.
The configuration in which the carcass ply is wound up from the outside to the inside in the widthwise direction in a manner as described above is advantageous in terms of the steering stability. However, the end portions of the carcass ply being wound get wrinkles easily because it is wound up in a direction in which the circumferential length is reduced. If such wrinkles are formed, unevenness results in the corresponding portion. Therefore, when the tire is deflected under load, a distortion concentrates on the portion having unevenness. Consequently, separation may occur and durability may be impaired correspondingly.